Catheters incorporating ultrasound imaging capabilities have been utilized for a number of years for gaining information about the internal condition of the human body. See, e.g., N. Bom, Early and Recent Intraluminal Ultrasound Devices, Int'l J. of Card. Imag., 4:79-88 (1989), reprinted in N. Bom, Intravascular Ultrasound (Kluwer Academic Publishers, 1989). Such imaging catheters, e.g., have been used to image areas in and around arteries, the heart, urinary tract, esophagus, large intestine, and other areas. In arterial (and other small diameter) applications, both the catheter and the ultrasound transducer elements of necessity must be very small in size, resulting in limited resolution and range (or "depth") of the resulting image.
Moreover, in some percutaneous procedures, the diameter of the catheter or similar instrument being used is not so much limited by the diameter of the area of interest (e.g., the aorta) as it is by the diameter of the entry passageway (such as the femoral artery); hence, at the area of interest the diameter of the instrument may be significantly smaller than the diameter of the passageway or cavity, exacerbating the problems resulting from the limited imaging range of the small diameter ultrasound transducer apparatus.